In variable cycle gas turbine engines, the amount of air flowing through bypass ducts is varied under different operating conditions to improve engine performance. In one embodiment of such engines, airflow is controlled by an annular sliding valve system, sometimes referred to as a variable area bypass injector (VABI), that is effective for controlling the amount of airflow in inner and outer annular bypass ducts.
The VABI system typically includes an axially translatable annular member. This member comprises either a cylindrical sleeve valve, or a synchronizing ring that uniformly positions a plurality of circumferentially disposed drop chute valve members for controlling the amount of flow through the ducts.
For example, a forward VABI comprising a cylindrical sleeve valve can be used for controlling the amount of airflow in the outer bypass duct that bypasses a combustor of the engine. A rear VABI comprising a cylindrical sleeve valve or drop chutes can be provided for injecting airflow from the outer bypass duct into a discharge flow from a core engine of the gas turbine engine.
Variable cycle engines including VABIs are disclosed in "Individual Bypass Injector Valves for a Double Bypass Variable Cycle Turbofan Engine", U.S. Pat. No. 4,175,384-Wagenknecht et al, "Variable Area Bypass Injector System", U.S. Pat. No. 4,072,008-Kenworthy et al, and "Actuation System For Use on a Gas Turbine Engine", U.S. Ser. No. 252,687-Nash et al, now U.S. Pat. No. 4,409,788 all incorporated herein by reference.
A VABI can also be used to vary the amount of bypass airflow injected into an afterburning section of a gas turbine engine. Such a VABI system is disclosed in "Variable Slot Bypass Injector System", U.S. Ser. No. 317,356, Vdoviak et al, incorporated herein by reference.
A variable cycle engine useful as an aircraft engine requires a relatively simple and lightweight actuation system for positioning of the vABI system. In this regard, a minimum number of actuators and linkages associated with the actuation system is preferred. However, the actuation system must be capable of transmitting sufficiently large force to the translating annular member for translating the member without allowing the member to tilt, and thus bind.
Prior art actuation systems typically include multiple radial shafts extending through an engine casing. These shafts can be driven by a plurality of actuators or, in the case where fewer actuators are used, synchronizing rings are used for uniformly transmitting the force from the actuators to all the radial shafts for translating the annular member thereof without binding. However, typical prior art actuation systems have substantial complexity and weight and therefore are undesirable.
Accordingly, it is an object of the present invention to provide a new and improved actuation system for a gas turbine engine.
Another object of the present invention is to provide an actuation system for translating an annular member in the gas turbine engine.
Another object of the present invention is to provide an actuation system having one actuator and a reduced number of members and linkages for translating the annular member.
Another object of the present invention is to provide a relatively simple and lightweight actuation system for axially translating an annular valve member of a variable area bypass injector in a gas turbine engine.